Feedstock for metal foil product and method of making thereof

ABSTRACT

The present invention discloses a product comprising a 1xxx, 3xxx and 8xxx series aluminum alloy made by a non-ingot casting process, where the aluminum alloy has a thickness of about 5 micrometers to about 150 micrometers for a foil product. The product has an O-temper tensile strength, O-temper elongation, and O-temper Mullen pressure that are at least 10% greater compared to the average values of the same alloy in O-temper cast using a slab or roll-casting process. The product is substantially free of pinholes caused by centerline segregation of intermetallic particles. In another embodiment, the present invention discloses a 8111 or 8921 aluminum alloy made by a non-ingot casting process, where the aluminum alloy has a thickness of about 5 micrometers to about 150 micrometers for a foil product. The product has an O-temper tensile strength, O-temper elongation, and O-temper Mullen pressure that are at least 10% greater than the average values of the same alloy in O-temper made from feedstock prepared by slab or roll casting processes. The product is substantially free of pinholes caused by centerline segregation of intermetallic particles.

BACKGROUND OF THE INVENTION

A feedstock is a material that needs to undergo further processingbefore it becomes a final product. In one embodiment, the end useapplication for these feedstock covers various products such aspackaging needs i.e. household foils. In another embodiment, thealuminum foil products made from the feedstock disclosed has improvedsurface characteristics and mechanical properties such as high burstpressure, high tensile strength, high yield strength and higherpercentage elongation at thin gauges.

SUMMARY OF THE INVENTION

In one embodiment, the present invention provides a feedstock product.In another embodiment, the product comprises a 1xxx, 3xxx and 8xxxseries aluminum alloy made by a non-ingot casting process where thealuminum alloy has a thickness of about 5 micrometers to about 150micrometers for a foil product. The product has an O-temper tensilestrength that is at least 10% greater compared to the average values ofthe same alloy in O-temper cast using a slab or roll-casting process.The product has an O-temper elongation that is at least 10% greatercompared to the average values of the same alloy in O-temper cast usinga slab or roll-casting process. The product has an O-temper Mullenpressure that is at least 10% greater compared to the average values ofthe same alloy in O-temper cast using a slab or roll-casting process.The product is substantially free of pinholes caused by centerlinesegregation of intermetallic particles.

In one embodiment, the product comprises an 8111 aluminum alloy made bya non-ingot casting process where the aluminum alloy has a thickness ofabout 5 micrometers to about 150 micrometers for a foil product. Theproduct has a tensile strength in O-temper that is at least 10% greaterthan the average values of standard 8111 alloy in O-temper. The producthas an elongation in O-temper that is at least 10% greater than theaverage values of standard 8111 alloy in O-temper. The product has aMullen pressure in O-temper that is at least 10% greater than theaverage values of standard 8111 alloy in O-temper. The product issubstantially free of pinholes caused by centerline segregation ofintermetallic particles.

In another embodiment, the product comprises an 8921 aluminum alloy madeby a non-ingot casting process where the aluminum alloy has a thicknessof about 5 micrometers to about 150 micrometers for a foil product. Theproduct has a tensile strength in O-temper that is at least 10% greaterthan the average values of standard 8921 alloy in O-temper. The producthas an elongation in O-temper that is at least 10% greater than theaverage values of standard 8921 alloy in O-temper. The product has aMullen pressure in O-temper that is at least 10% greater than theaverage values of standard 8921 alloy in O-temper. The product issubstantially free of pinholes caused by centerline segregation ofintermetallic particles.

Accordingly, it is one embodiment of the invention to provide afeedstock with improved properties.

These and other further embodiments of the invention will become moreapparent through the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the invention, reference is made to thefollowing description and the accompanying drawing(s), in which:

FIG. 1 is a flow chart showing the existing method of making foil andfin from roll cast feedstock;

FIG. 2 is a flow chart showing one embodiment of the method of makingfoil in accordance with the present invention;

FIG. 3 is three layered casting strip of one embodiment of the presentinvention; and

FIG. 4 is a photomicrograph at 100 times magnification of the transversesection of the as cast strip alloy 8921 of one embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following are the definitions of the terms used in this application.As used herein, the term “feedstock” means that the material that needsto undergo further processing before it becomes a final product such asa household foil.

As used herein, the term “aluminum alloy” means an aluminum metal withother elements. Elements may include copper, iron, magnesium, nickel,silicon, zinc, chromium, manganese, titanium, vanadium, zirconium, tin,and/or scandium. Elements are added to influence physical properties ofthe aluminum alloy and performance characteristics.

As used herein, the term “centerline segregation” means alignedintermetallic particles in the center plane of strip made byconventional roll casters. It can lead to tearing of the sheet duringrolling and results in poor mechanical properties in the final product.

As used herein, the term “refined microstructures” means microstructureswith fine grain size and fine constituents.

As used herein, the term “beta intermetallic phase particles” means rodlike particles of Al₉FeSi composition. These are brittle particles thatbreak up during rolling and result in inferior mechanical properties inthe final product. Their detrimental effects are eliminated byhomogenization treatments that convert the beta phase to the moreductile alpha phase.

As used herein, the term “in-line” means without intermediate coilingand uncoiling.

As used herein, the term “grain refiner” means a chemical compound suchas TiB₂, TiC or AlTi that helps create a finer grain structure in thecast metal.

As used herein, the term “Mullen burst pressure” means pressure at whicha sheet tears. It measures resistance to tearing.

As used herein, the term “substantially” means to a great extent ordegree.

As used herein, the term “non-ingot casting process” means any castingprocess that does not produce an ingot.

As used herein, the term “slab process” means a process that casts aslab between about 0.25 inches and about 8 inches in thickness.

As used herein, the term “roll-casting process” means casting a strip ofthickness of about 0.25 inches to about 0.5 inches at speeds of lessthan 10 feet per minute using convention roll casters at high rollseparating forces.

As used herein, the term “pinholes” means a small hole in a metal sheetor foil as measured in a light box.

As used herein, the term “hot rolling” means rolling of aluminum metalat an entry temperature above about 700° F.

As used herein, the term “warm rolling” means rolling of aluminum metalat an entry temperature range of about 350° F. to about 700° F.

As used herein, the term “cold rolling” means rolling of aluminum metalat a entry temperature below about 350° F.

In one embodiment, the present invention discloses a feedstock producedusing a method that includes producing a casting strip of a thickness ofless than about 6 mm from an aluminum alloy, hot rolling the castingstrip in-line to a thickness of no greater than about 1 mm, and coilingthe resultant strip to produce the feedstock product for a metal foil,where the cast strip is substantially free of beta intermetallic phaseparticles.

In another embodiment, the feedstock is further processed to provide ametal foil with improved mechanical properties and surfacecharacteristics.

In another embodiment, the feedstock product is then further processedby un-coiling the strip, cold rolling the feedstock strip to a requiredproduct thickness, and partially or fully annealing the final-gaugestrip to produce a metal foil.

FIG. 1 shows a flow chart outlining the principal steps for theconventional process of making foil and fin products from roll castfeedstock. In the initial step 10, the aluminum alloy is roll cast to athickness between about 6 mm and about 10 mm. The aluminum alloy castingstrip is then hot/warm coiled in-line 20 and then optionally separatelyhomogenized at around 430° C. to about 530° C. In the next step 40, thehomogenized coil is then un-coiled so that the aluminum alloy castingstrip may be cold rolled to an intermediate gauge in step 50. Theintermediate gauge strip is then intermediately annealed at 450° C. instep 60 and cold rolled to the final gauge of the foil. In the finalstep 80, the aluminum alloy casting strip is optionally either partiallyor fully annealed depending on the physical properties needed for theproduct.

In one embodiment, FIG. 2 shows a flow chart outlining the principalsteps of the present invention. The present invention eliminates thelengthy and expensive homogenization and/or intermediate anneal stepsnormally associated with the current methods of roll cast or ingotfeedstock and eliminates one or more cold rolling passes. Here, thefeedstock strip cast of thickness of less than about 6 mm material isproduced at high speeds in the first step 100. The aluminum alloymaterial is then hot rolled in-line in the second step 200 to athickness of at most about 1 mm at about 720° F. The feedstock materialis then hot/warm coiled in-line in the third step 300. This material isan embodiment of the feedstock of the present invention, provided forfurther off-line processing into a finished product. In such an off-lineoperation, the coil is then un-coiled in step 400 prior to being coldrolled in the fifth step 500 to finish gauge, which is the requiredproduct thickness. The finished gauge product may optionally besubjected to a partial or full anneal treatment in the sixth step 600depending on the application, or supplied in as-rolled condition

In the initial step, a strip of less than about 6 mm in thickness iscast. In one embodiment, a method of making the casting strip of athickness of less than about 6 mm from an aluminum alloy is done bycontinuously casting the aluminum alloy. This includes delivering moltenaluminum alloy juxtaposed and in communication with a pair ofwater-cooled rolls arranged in a generally horizontal plane. Thiscasting is done at high speeds, such as about 200 fpm (62 m/min). Moltenaluminum alloy from a reservoir is advanced towards a nip between therolls. Outer layers of solid aluminum alloy forms on each of the rolls,and a semi-solid aluminum layer is produced in the center between thesolid layers. The semi-solid layer includes a molten component and asolid component of broken dendritic arms detached from thesolidification front. The solid outer layers and the solid component ofthe semi-solid aluminum alloy pass through the nip such that a strip ofsolid aluminum alloy exits the nip. The strip exiting the nip includes asolid central layer sandwiched between the outer conforming layers ofaluminum alloy.

In another embodiment, a method of making the casting strip of athickness of less than about 6 mm from an aluminum alloy is by in one,continuous in-line sequence that includes the following steps: (a) a hotaluminum feedstock is hot rolled to reduce its thickness; (b) the hotreduced feedstock is thereafter annealed in-line without substantialintermediate cooling; (c) the annealed feedstock is thereafterimmediately and rapidly quenched to a temperature suitable for coldrolling; and (d) the quenched feedstock is subjected to cold rolling toproduce sheet having desired thickness and metallurgical properties.

The resulting casting strip produced has a refined microstructure andsurprisingly, is substantially free of beta intermetallic phaseparticles. This results in superior quality foil products.

Types of aluminum alloys that may be used in the present inventioninclude, but are not limited to, 1XXX, 3XXX, and 8XXX aluminum alloys(Aluminum Association designations). Note that 8921 and 8111 householdfoils are described in examples later.

In one embodiment, the thickness of the casting strip is less than about6 mm. In another embodiment, the thickness of the casting strip is fromabout 1 mm to about 5 mm. In a further embodiment, the thickness of thecasting strip is from about 2 mm to about 4 mm.

In the second step, the strip cast is then hot rolled in-line to adesired thickness with a minimum of 10% reduction in thickness at about720° F. in one embodiment of the present invention. The term “hot rolledin-line” is defined as any rolling of aluminum cast strip directly fromthe caster at a mill inlet temperature of above about 700° F. In oneembodiment, the temperature of the feedstock material after hot rollingis below about 700° F. at the coiler.

A combination of hot- and warm rolling steps in-line can be used toreduce the material to the desired thickness. This is limited only bythe number of mill stands in-line with the caster.

In the third step, the feedstock material is hot/warm coiled. In oneembodiment, the temperature of the feedstock material is below about700° F. at the coilers.

In the fourth step, the coil is un-coiled so that the aluminum alloycasting strip may be cold rolled to the required product thickness forthe fifth step. In one embodiment, cold rolling takes place between apair of rotating rolls at room temperature. In another embodiment, thecold rolling step may be broken down to various steps depending on theproduct thickness. For example, the feedstock material may be rolled toa breakdown gauge before rolling the feedstock material to the finalgauge needed.

Depending on the final gauge desired, this results in a foil producthaving a substantially uniform thickness between about 5 to about 150micrometers. Table 1 shows a comparison of properties of the householdfoil made from the present invention of 8921 aluminum alloy with atypical commercial household aluminum foil.

TABLE 1 anneal thickness tensile strength yield strength elongationMullen product F./hr inch ksi ksi (min.) % psi Micromill 8921 550 F./4hr 0.000568 20.8 17.0 5.9 21.3 Micromill 8921 600 F./4 hr 0.000628 20.615.4 6.8 23.8 Micromill 8921 650 F./4 hr 0.000606 19.7 14.9 6.2 22.6ReynoldsWrap 0.000634 12.3 6.6 5.1 13.7 anneal thickness tensilestrength yield strength elongation Mullen C./hr μm MPa MPa % kPaMicromill 8921 288 C./4 hr 14.4 143.4 117.2 5.9 146.8 Micromill 8921 316C./4 hr 16.0 142.0 106.2 6.8 164.1 Micromill 8921 343 C./4 hr 15.4 135.8102.7 6.2 155.8 ReynoldsWrap 16.1 84.8 45.5 5.1 94.4 Notes: 1.ReynoldsWrap values are averages for the standard product sold underthis brand name. 2. Yield strength is not specified for household foil.

Table 2 shows a comparison of properties of the household foil made fromthe present invention of 8111 aluminum alloy with a typical commercialhousehold aluminum foil.

TABLE 2 anneal thickness tensile strength yield strength Mullen productF./hr inch ksi ksi elongation (min.) % psi Micromill 8111 525 F./4 hr0.000572 20.6 17.4 3.1 12.9 Micromill 8111 600 F./4 hr 0.000599 15.1 8.05.3 12.0 Micromill 8111 650 F./4 hr 0.000610 14.0 6.8 5.8 16.0 ReynoldsWrap (mean values) 0.000634 12.3 6.6 5.1 13.7 Specifications 0.00064 +/−10% 11.2-12.7 4.2 11.5 anneal thickness tensile strength yield strengthMullen C./hr μm MPa MPa elongation (min.) % kPa Micromill 8111 274 C./4hr 14.5 142.0 120.0 3.1 88.9 Micromill 8111 316 C./4 hr 15.2 104.1 55.25.3 82.7 Micromill 8111 343 C./4 hr 15.5 96.5 46.9 5.8 110.3 ReynoldsWrap (mean values) 16.1 84.8 45.5 5.1 94.4 Specifications 16.3 +/− 10%77.2-87.6 4.2 79.3 Notes: 1. Reynolds Wrap values are averages for thestandard product sold under this brand name. 2. Yield strength is notspecified for household foil.

In the fifth step, the finished gauge product may optionally besubjected to a partial or full anneal treatment depending on theapplication or supplied in as-rolled condition.

The casting strip is substantially free of beta intermetallic phaseparticles which results in a foil that is also free of betaintermetallic phase particles. Determination of the presence of betaintermetallic phase particles is conducted by microscope.

In one embodiment, the present invention provides a method of makingfeedstock for aluminum foil without the use of a grain refiner,intermediate anneals or homogenization. This results in improvedproperties of the resultant aluminum foils for the same alloy. Forexample, some of the improved alloy properties include a higherstrength, ductility and burst pressure. Note that this method of makingfeedstock for metal foil may be used to manufacture fin products.

In another embodiment, the present method produces a feedstock productwith improved properties.

In one embodiment, the product comprises a 1xxx, 3xxx and 8xxx seriesaluminum alloy made by a non-ingot casting process where the aluminumalloy has a thickness of about 5 micrometers to about 150 micrometersfor a foil product. The product has an O-temper tensile strength, anO-temper elongation, and an O-temper Mullen pressure that are at least10% greater compared to the average values of the same alloy in O-tempercast using a slab or commercially available roll-casting process. Theproduct is also substantially free of pinholes caused by centerlinesegregation of intermetallic particles.

In another embodiment, the product comprises a 8111 aluminum alloy madeby a non-ingot casting process where the aluminum alloy has a thicknessof about 5 micrometers to about 150 micrometers for a foil product. Theproduct has a tensile strength in O-temper, an elongation in O-temper,and a Mullen pressure in O-temper that are at least 10% greater than theaverage values of standard 8111 alloy in O-temper. The product issubstantially free of pinholes caused by centerline segregation ofintermetallic particles. The product demonstrates the same foldabilityas ReynoldsWrap®.

In another embodiment, the product comprises an 8921 aluminum alloy madeby a non-ingot casting process where the aluminum alloy has a thicknessof about 5 micrometers to about 150 micrometers for a foil product. Theproduct has a tensile strength in O-temper, an elongation in O-temper,and a Mullen pressure in O-temper that are at least 10% greater than theaverage values of standard 8921 alloy in O-temper. The product issubstantially free of pinholes caused by centerline segregation ofintermetallic particles in the feedstock material.

Examples of the improved properties of the feedstock products for the8921 aluminum alloy may be found in Table 1. Examples of the improvedproperties of the feedstock products for the 8111 aluminum alloy may befound in Table 2.

FIG. 3 shows a three layered casting strip 11 produced by the presentmethod. Casting strip 11 includes an upper and lower shell 12 and 13 anda central layer 14 which sandwiched between the upper and lower shell 12and 13, respectively. The center layer is substantially free of harmfulintermetallic particle stringers.

FIG. 4 shows a photomicrograph at 100 times magnification of atransverse section of an as-cast strip of alloy 8921 produced accordingto the present invention. This photomicrograph shows refinedmicrostructures, fine grains and no centerline segregation.

In one embodiment, the non-ingot casting process is the method of makinga feedstock for metal foil described above.

EXAMPLE 1

A sample of alloy 8921 was initially strip cast to a thickness of 2.7 mmand then was hot and warm rolled in line to about 0.64 mm in two millstands. The metal was coiled at 325° F. Alloy 8921 was then un-coiledand subsequently cold rolled to foil gauge, a thickness of 16 μm inmultiple rolling passes.

EXAMPLE 2

A sample of alloy 8111 was strip cast to a thickness of 2.5 mm and thenwas hot and warm rolled in line to about 0.64 mm in two mill stands.Alloy 8111 was then coiled at 325° F. Alloy 8111 was then un-coiled andsubsequently cold rolled to foil gauge of 16 μm in multiple rollingpasses.

The final anneal for Example 1 was done at 525, 600 and 650° F. with ahold time of 4 hours. The final anneal for Example 2 was done at 550,600 and 650° F. with a hold time of 4 hours. Mechanical propertyevaluations were carried out by standard ASTM procedures E345-93. Mullentests were done according to ASTM #774-97. Pinhole determination wasdone by ASTM B926-03.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any and all equivalents thereof.

1. A product comprising: a 1xxx, 3xxx and 8xxx series aluminum alloymade by a non-ingot casting process, wherein the aluminum alloy has athickness of about 5 micrometers to about 150 micrometers for a foilproduct, wherein the product has an O-temper tensile strength that is atleast 10% greater compared to the average values of the same alloy inO-temper cast using a slab or roll-casting process, wherein the producthas an O-temper elongation that is at least 10% greater compared to theaverage values of the same alloy in O-temper cast using a slab orroll-casting process, wherein the product has an O-temper Mullenpressure that is at least 10% greater compared to the average values ofthe same alloy in O-temper cast using a slab or roll-casting process,wherein the product is substantially free of pinholes caused bycenterline segregation of intermetallic particles.
 2. A productcomprising: an 8111 aluminum alloy made by a non-ingot casting process,wherein the aluminum alloy has a thickness of about 5 micrometers toabout 150 micrometers for a foil product, wherein the product has atensile strength in O-temper that is at least 10% greater than theaverage values of standard 8111 alloy in O-temper, wherein the producthas an elongation in O-temper that is at least 10% greater than theaverage values of standard 8111 alloy in O-temper, wherein the producthas a Mullen pressure in O-temper that is at least 10% greater than theaverage values of standard 8111 alloy in O-temper, wherein the productis substantially free of pinholes caused by centerline segregation ofintermetallic particles.
 3. A product comprising: an 8921 aluminum alloymade by a non-ingot casting process, wherein the aluminum alloy has athickness of about 5 micrometers to about 150 micrometers for a foilproduct, wherein the product has a tensile strength in O-temper that isat least 10% greater than the average values of standard 8921 alloy inO-temper, wherein the product has an elongation in O-temper that is atleast 10% greater than the average values of standard 8921 alloy inO-temper, wherein the product has a Mullen pressure in O-temper that isat least 10% greater than the average values of standard 8921 alloy inO-temper, wherein the product is substantially free of pinholes causedby centerline segregation of intermetallic particles.